Results from the TH3RESA study show that Kadcyla (chemical name: T-DM1 or ado-trastuzumab emtansine), a targeted therapy medicine, improved the time women diagnosed with advanced-stage HER2-positive disease lived without the cancer growing (disease-free survival) compared to a treatment of their doctor’s choice.

The results were presented on Sept. 28, 2013 at the European Cancer Congress in Amsterdam.

Kadcyla is a combination of Herceptin (chemical name: trastuzumab) and the chemotherapy medicine emtansine. In Kadcyla, the emtansine is attached to the Herceptin. In earlier studies on Kadcyla, it was reported that the chemotherapy medicine maytansine was attached to Herceptin to form Kadcyla. Emtansine is a derivative of maytansine.

Kadcyla is approved by the U.S. Food and Drug Administration (FDA) to treat HER2-positive metastatic breast cancer that has previously been treated with Herceptin and a taxane chemotherapy.

Herceptin is approved by the FDA to treat advanced-stage, HER2-positive breast cancers and to lower the risk of recurrence of early-stage, HER2-positive breast cancer with a high risk of recurrence. HER2-positive breast cancers make too much of the HER2 protein. The HER2 protein sits on the surface of cancer cells and receives signals that tell the cancer to grow and spread. About one out of every four breast cancers is HER2-positive. Herceptin works by attaching to the HER2 protein and blocking it from receiving growth signals.

Emtansine, like some other chemotherapy medicines, disrupts the way cells grow. Emtansine isn’t a targeted medicine, which means it can affect healthy cells as well as cancer cells.

Kadcyla was designed to deliver emtansine to cancer cells in a targeted way by attaching emtansine to Herceptin. Herceptin then carries emtansine to the HER2-positive cancer cells.

In the TH3RESA study, researchers wanted to see if Kadcyla would offer more benefits to people diagnosed with advanced-stage HER2-positive breast cancer who had received at least two previous treatments for the disease, including Herceptin, Tykerb (lapatinib), and a taxane chemotherapy, than their doctor’s choice of treatments for advanced-stage HER2-positive disease.

So the researchers randomly assigned 602 people diagnosed with advanced-stage HER2-positive breast cancer to receive either:

an intravenous infusion of Kadcyla every 3 weeks

a treatment of their doctor’s choice, which included Herceptin and chemotherapy, only chemotherapy, Tykerb and Herceptin, Tykerb and chemotherapy, and hormonal therapy and Herceptin

The people who got Kadcyla lived about 3 months longer without the cancer growing than the people who got the treatment of their doctor’s choice (6.2 months compared to 3.3 months).

People who were receiving the treatment of their doctor’s choice and had the cancer grow had the option of switching to the Kadcyla group. So far, 44 people have switched.

Severe side effects are unfortunately common with many cancer treatments. About 32% of the people who got Kadcyla had severe side effects compared to 43% of the people who got their doctor’s choice of treatment. The most common side effects of Kadcyla were:

low platelet count

low red blood cell count

higher liver enzyme levels

fatigue

difficulty breathing

If you’re being treated for HER2-positive advanced-stage breast cancer that has stopped responding to a standard targeted therapy regimen, you and your doctor may be considering other treatment options. You may want to ask your doctor about Kadcyla and whether it might be a good treatment option for you based on your unique situation.